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Java Arrays

  • An array is a collection of similar types of data having contiguous memory allocation.

  • The indexing of the array starts from 0., i.e 1st element will be stored at the 0th index, 2nd element at 1st index, 3rd at 2nd index, and so on.

  • The size of the array can not be increased at run time therefore we can store only a fixed size of elements in array.

  • Use Case: Storing marks of 5 students

  • Accessing Array Elements :

    Array elements can be accessed as follows,

    /* marks[0] = 100       //Note that index starts from 0
    marks[1] = 70
    marks[4] = 98 */

    So in a nut shell, this is how array works:[] marks; //Declaration!
    2.marks = new int[5]; //Memory allocation![] marks = new int[5]; //Declaration + Memory allocation![] marks = {100,70,80,71,98} // Declare + Initialize!
    Note : Array indices start from 0 and go till (n-1) where n is the size of the array.

    Array length :

    Unlike C/C++, we don't need to use the sizeof() operator to get the length of arrays in Java because arrays are objects in Java therefore we can use the length property.

    marks.length //Gives 5 if marks is a reference to an array with 5 elements

    Displaying an Array :

    An array can be displayed using a for loop:

    for (int i=0; i<marks.length; i++)
                Sout(marks[i]);    //Array Traversal


    public class cwh_26_arrays {
        public static void main(String[] args) {
            /* Classroom of 500 students - You have to store marks of these 500 students
            You have 2 options:
            1. Create 500 variables
            2. Use Arrays (recommended)
            // There are three main ways to create an array in Java
            // 1. Declaration and memory allocation
            // int [] marks = new int[5];
            // 2. Declaration and then memory allocation
            // int [] marks;
            // marks = new int[5];
            // Initialization
            // marks[0] = 100;
            // marks[1] = 60;
            // marks[2] = 70;
            // marks[3] = 90;
            // marks[4] = 86;
            // 3. Declaration, memory allocation and initialization together
            int [] marks = {98, 45, 79, 99, 80};
            // marks[5] = 96; - throws an error




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